1. Field of the Invention
The present invention generally relates to a handwriting input apparatus, and more particularly to a handwriting input apparatus with a programmable charging circuit.
2. Description of the Related Art
Electromagnetic type of handwriting input apparatus such as a tablet, or a digitizer usually further includes a stylus or an electromagnetic pen. An electromagnetic pen generally includes a circuit with capacitors and inductors. A digitizer generally has a plurality of antenna loops, analog to digital converter, amplifiers, a processor or a control IC on a printed circuit boards, which are used for sensing electromagnetic signals from the electromagnetic pen, and for calculating the position, trace, variation of the frequency of the electromagnetic pen through a calculating process to display the position, and trace of the electromagnetic pen on a display device.
The operating principle of an electromagnetic type handwriting input apparatus primarily involves a circuit board having a plurality of antenna loops arranged along the x axis or y axis, and an electromagnetic pen which is able to transmit electromagnetic signals to perform input actions. Current electromagnetic input apparatus, depending on the different types of electromagnetic pens, can be categorized as one type used with an electromagnetic pen with a battery and another type used with an electromagnetic pen without battery. The electromagnetic input technology applied in the electromagnetic input apparatus which uses an electromagnetic pen with a battery is known as active type electromagnetic input technology. Since the electromagnetic pen is able to operate by its own power to independently transmit signal, the electromagnetic input apparatus using active electromagnetic input technology does not need to transmit extra energy to power up the electromagnetic pen.
The electromagnetic input apparatus which uses an electromagnetic pen with a battery usually has a charger function to charge the electromagnetic pen. The invention provides a handwriting input apparatus with a programmable charging circuit and an electromagnetic pen so that the charging of the electromagnetic pen is able to be programmed and controlled according to the requirement, and the charging of the electromagnetic pen is more convenient and efficient.